A number of different video encoding standards have been established for encoding digital video sequences. The Moving Picture Experts Group (MPEG), for example, has developed a number of standards including MPEG-1, MPEG-2 and MPEG-4. Other examples include the International Telecommunication Union (ITU) H.263 standard, and the emerging ITU H.264 standard. These video encoding standards generally support improved transmission efficiency of video sequences by encoding data in a compressed manner.
Video telephony (VT), as an example, permits users to share video and audio information to support applications such as videoconferencing. Exemplary video telephony standards include those defined by the Session Initiation Protocol (SIP), the ITU H.323 standard, and the ITU H.324 standard. In a VT system, users may send and receive video information, only receive video information, or only send video information. A recipient generally views received video information in the form in which it is transmitted from a sender.
Encoded video can suffer from temporal quality degradation due to frame dropping. Frame dropping can result from a variety of factors such as frame skipping, frame rate down-sampling and channel packet losses. In general, frame skipping tends to have a greater impact on temporal quality degradation than frame rate down-sampling or channel packet losses. In the case of substantial frame dropping, the viewer may observe frame freezing because most video decoders automatically duplicate the last frame received before a dropped frame, and present the duplicate frame in place of the dropped frame while maintaining the same frame rate.
The duplication associated with frame dropping causes a temporal discontinuity often referred to as “jerkiness.” Jerkiness tends to be disconcerting to a viewer of the decoded video. In viewing a jerky video sequence, the viewer experiences discomfort not only due to the amount of dropped frames, but also due to the temporal quality fluctuation between dropped and non-dropped frames. The human visual system tends to have a very high sensitivity to the quality contrast of the current frame to its neighboring frames.